The proposed-updates mechanism

All changes to the released, stable (and oldstable)
distribution go through an extended testing period before they are accepted
into the archive. Each such update of the stable (oldstable) release is called
a point release.

Preparation of point releases is done through the proposed-updates
mechanism. Updated packages are uploaded to a separate queue called
p-u-new (o-p-u-new), before they are accepted in
proposed-updates (oldstable-proposed-updates).

To use these packages with APT, you can add the following lines to your
sources.list file:

# proposed updates for the next point release
deb http://ftp.us.debian.org/debian wheezy-proposed-updates main contrib non-free

Note that the /debian/ mirrors will
have this, it is not necessary to use this particular one, the above choice
of ftp.us.debian.org is just an example.

New packages can arrive into proposed-updates when Debian developers
upload them either to proposed-updates (oldstable-proposed-updates),
or to stable (oldstable).
The upload process is described in the Developer’s Reference.

It should be noted that packages from
security.debian.org are copied into the
p-u-new (o-p-u-new) directory automatically. At the same time, packages
that are uploaded directly to proposed-updates (oldstable-proposed-updates) are
not monitored by the Debian security team.